FSH RECEPTOR GENE-EXPRESSION DURING OVARIAN FOLLICLE DEVELOPMENT IN SHEEP

A key question in elucidating the role of FSH in ovarian function is t o determine when during follicular growth the FSH receptor first appea rs. The aim of this study was to examine the site and time of FSH rece ptor gene expression during early follicular growth. This study was ca rried out on ovaries of adult sheep during the luteal and prostaglandi n-induced follicular phase of the oestrous cycle and also on ovaries o f fetal sheep at 90, 100, 120 and 135 days of gestation (term=day 147) . Using reverse transcription-PCR and a set of PCR primers spanning ex ons 8/9/10, two partial FSH receptor cDNAs (500 and 310 bp) were isola ted from adult sheep ovary. It was shown by sequencing that exon 8 was deleted in the 310 bp cDNA, implying that this was part of an alterna tively spliced FSH receptor transcript. Using RNA in situ hybridisatio n on ovaries of adult sheep, FSH receptor mRNA was observed in granulo sa cells of early preantral follicles with one to two cell layers and it was seen that gene expression continued throughout folliculogenesis into advanced stages of atresia. Moreover, in the fetus, FSH receptor gene expression was detected in follicles with two or more layers of granulosa cells in ovaries taken at 100, 120 and 135 days of gestation . These results suggest that the FSH receptor gene is expressed after the granulosa cells of a follicle have begun to divide but not during the earliest stages of follicle growth, namely the transformation of a primordial follicle to a primary follicle.